Known aerosol containers are made of a metal sheet which is wrapped into a cylindrical body so that overlapping edges may be welded into a seam. Shaped caps are fitted onto the ends in a sealed manner, and one of these seals is typically provided with a dispensing valve. Such a container is useful for containing a liquid product and a pressurized propellant.
It is desirable to use tinplated steel blanks to form cans in appropriate applications because such a material is inexpensive. Tinplated steel is suitable for a container so long as the contents do not corrode the tin and steel. Unfortunately, tinplated steel has been found unsuitable for many aerosol dispensing container applications because it tends to corrode when exposed to certain corrosive compounds found in certain applications such as saline solutions, hair mousse treatments, and dimethyl ether (DME) propellants. In an attempt to avoid corrosion, aerosol cans have typically been produced from aluminum or coated with thin organic coatings, which, although they exhibit good corrosion resistance, are also relatively expensive. However, constructing the body from tinplated steel requires some means of preventing exposure of the metal to the corrosive contents.
One known aerosol container prevents the product from contacting and corroding the metal container body using a collapsible bag for housing the product. The propellant, contained within the container body, exteriorly surrounds the bag and selectively compresses the bag to dispense the product in response to a release valve. Unfortunately, the presence of the bag requires additional components and assembly steps, which also increases costs.
Another means of preventing corrosion of the container body is to laminate or coat its interior and/or exterior surface with a corrosion-resistant layer. For example, certain varnishes, paints, inks or plastic laminates are suitable to protect a metal blank such as tinplated or tin-free steel from corrosion, so long as the corrosion-resistant layer is compatible with the product contents. Corrosion-resistant layers, such as coatings or laminates, if present at the overlapping weld site, however, introduce a foreign substance that can weaken the weld or prevent an effective weld from forming. Therefore, the overlapping area must be free from the coating or laminate material. Accordingly, it is known to apply the corrosion-resistant layer partially to the metal, leaving exposed portions or strip-shaped areas. For example, a lacquer coating or laminate can be applied to the metal blank in a striped pattern to leave exposed metal strips at the area to be overlapped and welded. After welding, a supplemental corrosion-resistant layer can be applied over the seam to prevent it from corroding. The process of applying a corrosion-resistant layer to only a predetermined portion of a sheet, however, can be expensive.
It is also known to coat or laminate the entire surface of the metal sheet, then remove portions of the corrosion-resistant layer to expose areas at the sites of metal to be welded. This is conventionally done by mechanical means, such as by sanding, grinding, milling, scraping, or by burning or applying heat, such as with a laser. These conventional layer-removal means do not provide reliably clean surfaces suitable for welding, and may also create undesirably airborne dust or smoke. Moreover, these require potentially dangerous equipment.